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Date: Wed, 29 Jan 2020 12:19:26 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>
Cc: Andrew Lunn <andrew@...n.ch>,
"David S. Miller" <davem@...emloft.net>,
Florian Fainelli <f.fainelli@...il.com>,
Heiner Kallweit <hkallweit1@...il.com>,
netdev <netdev@...r.kernel.org>,
"ykaukab@...e.de" <ykaukab@...e.de>
Subject: Re: [PATCH v2 2/2] dpaa_eth: support all modes with rate adapting PHYs
Hi Madalin,
On Wed, 29 Jan 2020 at 11:09, Madalin Bucur (OSS)
<madalin.bucur@....nxp.com> wrote:
>
> > -----Original Message-----
> > From: Vladimir Oltean <olteanv@...il.com>
> > Sent: Tuesday, January 28, 2020 5:42 PM
> > To: Andrew Lunn <andrew@...n.ch>
> > Cc: Madalin Bucur (OSS) <madalin.bucur@....nxp.com>; David S. Miller
> > <davem@...emloft.net>; Florian Fainelli <f.fainelli@...il.com>; Heiner
> > Kallweit <hkallweit1@...il.com>; netdev <netdev@...r.kernel.org>;
> > ykaukab@...e.de
> > Subject: Re: [PATCH v2 2/2] dpaa_eth: support all modes with rate
> > adapting PHYs
> >
> > Hi Andrew,
> >
> > On Mon, 27 Jan 2020 at 18:04, Andrew Lunn <andrew@...n.ch> wrote:
> > >
> > > > Is this sufficient?
> > > > I suppose this works because you have flow control enabled by
> > default?
> > > > What would happen if the user would disable flow control with
> > ethtool?
> > >
> > > It will still work. Network protocols expect packets to be dropped,
> > > there are bottlenecks on the network, and those bottlenecks change
> > > dynamically. TCP will still be able to determine how much traffic it
> > > can send without too much packet loss, independent of if the
> > > bottleneck is here between the MAC and the PHY, or later when it hits
> > > an RFC 1149 link.
> >
> > Following this logic, this patch isn't needed at all, right? The PHY
> > will drop frames that it can't hold in its small FIFOs when adapting a
> > link speed to another, and higher-level protocols will cope. And flow
> > control at large isn't needed.
>
> I'm afraid you missed the patch description that explains there will be
> no link with a 1G partner without this change:
>
So why not just remove that linkmode_and() at all, then?
What is it trying to accomplish, anyway? Avoiding the user from
shooting themselves in the foot maybe?
> << After this
> commit, the modes removed by the dpaa_eth driver were no longer
> advertised thus autonegotiation with 1G link partners failed.>>
>
> > What I was trying to see Madalin's opinion on was whether in fact we
> > want to keep the RX flow control as 'fixed on' if the MAC supports it
> > and the PHY needs it, _as a function of the current phy_mode and maybe
> > link speed_ (the underlined part is important IMO).
>
> That's a separate concern, by default all is fine, should the user want to
> shoot himself in the foot, we may need to allow him to do it.
>> > >
> > > Andrew
> > >
> >
> > Thanks,
> > -Vladimir
-Vladimir
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